Filter plate with spacing means



United States Patent [72] lnventors Oswald Busse;

Hugo Klesper, Michelbach, Germany [21] Appl. No. 819,929 [22] FiledApril 28, 1969 [45] Patented Dec. 1, 1970 [73] Assignee Passavant WerkeMichelbacher, Hutte, Germany [32] Priority June 6, 1968 [33] Germany[31] No. 1,761,556

[54] FILTER PLATE WITH SPACING MEANS 7 Claims, 5 Drawing Figs.

[52] U.S.Cl 210/229,

210/231 [51] lnt.Cl B0ld 25/12 [50] Field ofSeareh 210/227, 229, 231,486

[56] 'References Cited UNITED STATES PATENTS 298,758 5/1884 Johnson210/231 Primary Examiner Reuben Friedman Assistant Examiner-C. M. DitlowAnorney Larson, Taylor & Hinds ABSTRACT: A filter plate for a filterpress, the plate including raised parts projecting outwardly from theinner portions of the plate within the bordering frame part andincluding spacing elements located at the outermost ends of the spacingelements. A filter cloth extends over the inner portion and passesbetween the spacing elements and the surface of the inner portion. Onespacing element may be mounted on each end ofa pin extending through thefilter plate.

Patented Dec. 1, 191.0 3,543,938

She'et of 3 IZA i IZA l 3 INVENTORS OSWALD BUSSE HUGO KLESPER mo uszjaf/v v ATTORNEYS Patented Dec.1, 1970 3 ,543,938

Sheet 2 of a INVENTORS OSWALD BUSSE HUGO KLESPER ATTOR N EYS Patent edDec. 1, 1970 OSWALD BUSSE I uso KLESPER 1hr $602 Ja /er ATTORNEYS FILTERPLATE WITH SPACING MEANS BACKGROUND OF THE INVENTION This inventionrelates to filter plates, and in particular it relates to filter platesof the type for use in frame or chamber type filter pressesconventionally used, for example, for dewatering sewage sludge.

In filter presses of the present type, unbalanced pressure conditionsoften exist on opposite sides of a given filter plate. This can causethe plates to bend, thereby damaging the plates. This problem isespecially acute for large plates and/or plates placed under highpressure conditions. To avoid this problem, it is known to provide abracing structure between the filter plates such as raised cams or ribsor the like, protrud ing from the surface of the central portion of theplates towards the adjacent plates. These known bracing structures haveusually been formed as a part of the filter plate itself; and the filtercloth which normally covers the filter plate has then been spread acrossthe said raised structures. However, this arrangement has thedisadvantage that the filter cloth must pass over the outermost ends ofthe raised bracing structure. This caused weakening of the filter cloth.This resulted for at least two reasons. First, it was necessary tostretch the filter cloth in order to pass it over the raised bracingstructure. Secondly, considerable friction is generated at the pointswhere the filter cakes pass over the, outermost points of the bracingstructure as these points are subjected to frictional wear as thefinished filter cakes slide downwardly as the plates are separated atthe conclusion of the pressing operation.

One solution to this'problem has been to provide the bracing structureas a ring extending outwardly adjacent the central opening in the filterplate-which is normally provided for introducing influent into the spacebetween the filter plates. However, this arrangement has thedisadvantage that it considerably narrows the fiow area available forthe introduction of influent liquid. This could block the flow of fiuidand permit additional pressure differences to exist, thereby furtherincreasing the danger of damage to the filter plates.

Thus, there exists a need for a new and improved means for bracing thefilter plates relative to eachother during the pressing operationwithout damaging the filter cloths or without concurrently increasingthe risk of danger to the filter plates themselves.

SUMMARY OF THE INVENTION Thus, a purpose of the present invention is toprovide a new and improved filter plate which overcomes disadvantages offilter plates known heretofore.

This purpose is achieved in accordance with the present invention byproviding an arrangement whereby the bracing structure comprisesseparate spaced elements located on and projecting outwardly from theframe elements, whereby the filter cloths extend between these spacingelements and the surface of the filter plate. With this arrangement, itis not necessary to stretch the filter cloth over the spacing elementsand it is not necessary to locate portions of the filter cloth at theoutermost points of the spacing elements where they would be subjectedto frictional forces as discussed above. Further, this arrangementeliminates much of the frictional force that would be applied to theentire area of the filter cloths during the downward sliding movement ofthe filter cake. With this arrangement, because of the spacing elements,the filter cake does not drop until the plates are moved apartsufficiently for the filter cake to drop beyond the outermost point ofthe spacing elements. Not only does this reduce wear on the filtercloth. but it renders the operation of removing the filter cake moreefficient as it permits a more smooth movement ofthe filter cake.

According to a preferred embodiment of the present invention, thespacing elements are located at suitable points between the centralinfluent bore of the filter plate and the raised outer frame of thefilter plate. This is the thin inner portion of the filter plate whereits structural rigidity is minimal and where the need for bracing isgreatest.

Preferably, raised bosses are formed on the said inner portion, theouter surface of these bosses being plane and being located onlyslightly outwardly from the remaining surface of the inner portion. Thefilter cloth must pass over these plane surfaces and the spacingelements are positioned on the outside of the filter cloth and includemeans passing through the filter cloth and connected to the boss. Thus.since the filter cloth must pass over these bosses, it is preferable tokeep their height to a minimum.

In a preferred arrangement of the present invention alined bosses areprovided on opposite sides of the inner portion of the filter plate andan aperture is formed through the said' inner portion of the filterplate passing through both of the alined bosses. A cylindrical pin,which may be hollow to permit fluid flow across the inner portion, isthen placed through the aperture and through the filter cloths,andspacing elements are then attached to both ends of this pin.

For purposes of definition, the-plane passing through the center of thefilter plate and parallel to the large generally flat sides of thefilter plate will be referred to hereinafter as the center plane. Inplate filters of this type, the outer frame generally extends outwardlyfrom the center plane an amount greater than the inner portion. Withthis arrangement, contact between adjacent plates is made at the outerframes while the spaces between the reduced inner portions form thechambers in which the influent liquid is received.

In a preferred arrangement of the invention the height of the spacingelements from the center plane should be no greater than the height ofthe outer frame structure from the center plane so that in the rest orunloaded condition of the filter press, with the filter plates incontact with each other. a

distance of 0.1 to 0.5 mm. is provided. Preferably, this clearance is0.1 to 0.3 mm. Preferably, all of the elements should be of the sameheight with a tolerance of up to 0.3 mm., but preferably up to 0.2 mm.This permits sufficient engagement of the outer frame member while itdoes not cause too high a surface pressure to be exerted on the portionof the filter cloth located between the spacing elements and the raisedbosses during the pressing operation.

ln accordance with another feature of the present invention the face ofthe spacing elements facing the filter cloth are preferably larger thanthe outermost end of the spacing eleof a truncated cone. Thisarrangement also provides 'a more rapid and uniform removal of thefilter cake from the filter.

cloth. Also, the larger area against the cloth reduces the pres. sureagainst the filter cloth.

Thus, it is a purpose of this invention to provide a new and improvedfilter plate which overcomes disadvantages of previously known filterplates.

It is another object of this invention to provide a new and improvedfilter plate, in a filter press of the type described, wherein wear uponthe filter cloth is substantially reduced.

It is another object of this invention to provide a filter plate for afilter press of the type described, having spacing elements projectingoutwardly from the inner portion of the plate and wherein the filtercloth is positioned between the spacing elements and the surface of thefilter plate.

It is another object of this invention to provide a new and improvedarrangement for mounting spacing elements on a filter plate for use in afilter press of the type described.

Other objects and the intended advantagesof the present invention willbecome apparent from the detailed description to follow together withthe accompanying drawings.

BRIEF SUMMARY OF THE DRAWINGS helper-n;- i

I oE'rAiLED oEscRiP'rioN OF THE PREFERRED EMBODIMENT like numerals areused to represent like elements throughout; and in FIG. Sthesamenumerals include a prime to indicate similar elements on an adjacentfilter plate.

' FIG 1 illustrates, schematically, a filter press of the type in which'th'efilter'plate of the present invention would be used. A" plurality"of suchplates 1 are positioned with their large facesitowa'rds'eiachother. The plates are supported on suitable m e'anssuchfa's support rods15., For example, the support rods ISIm'ay comprise a pair of parallelpoles onto which the slots 12A (see FIG. 2 are-mounted. A force P wouldthen be applied to end structures 20 for forcing the filter plates 1together. i

-,Referrin g' now to FIGS. 2 through 5,the filter plate 1 includes-araised outer frame which extends about the periphery of thefilter plate.When the plates are mounted on thefilte'r press,itisthese raised outerframes which engage the raised outer frarnes of adjacentsfilter platesthrough which most of the pressing force is'transmitted. Thus, it can beseen that if pressure differential forces across a filter plate causethat filterplate to be misaligned, relative to the adjacent filterplates, iiis likely that the outer frame 5 could be bent, and this wouldof course render the filter plate inoperable.

v O'ver theinlarge; generally flat surfaces the filter plates includefilter cloths 3, who shown in the upper right hand portioriof FIG 2,'andshown alsoin H65. 3 and 5, through which the filter liquid passes; Thesurface of the filter plate includes a pluralityof downwardlyextendinggrooves 2 for drainage of the filteredliquid which liquidisthen discharged from. the spacebetween'the filter plate through openingin the frame Sas' shown in FlG.2.

I Asses: shown in-FlG. 5, a chamber 11 is formed between adjacent filterplates. lnfluent liquid is introduced ,to this chamber, through acentral bore4 which is visible in F IG. 2.

a if! accordancewith'a main feature of the present invention,thefilter'pla tes are provided with a plurality of spacing elements6.-For this purpose the'filter plates are provided with raised bosses 13formed on the surface of the filter plate. Preferably, the outersurfaces-of these bosses are plane since this wiIlrninimiZe wear uponthe filter cloths which pass thereover. A bore 16 passes through thefilter plate 1 at the bosses 135A pin 7 is then passed through this bore16 and also through alined aprtures formed in the filter cloths 3. Asillustrated inFlG. 4, the element 7 may be a hollow elongated split ringwithoutward resilience so that when the ring is placed in the bore itexpands outwardly, whereby it is held tightly in the bore 16 .Theelongated slot 9 is shown in FIG. 4. The, spacing elements 6-maytthenbeattached to either end of the pin 7 any suitable means such -as screwthreads, spring and groove, etc. Further, in a preferred arrangement ofthe present inventi'omth'e pin 7 will be hollow and include a bore 8which passes completely through thepin thereby placing the two sides ofthe filter plate 1 into fluid communication with each other. This hasthe advantage of providing additional passages for equalizing the fluidpressure on either side of the filter plate 1. 3

As noted above, the filter cloths 3 should be stretched aslittleaspossible. Consequently, it is preferable to. maintain the heightof bosses 13as low aspossible to avoid this stretching of the filtercloths 3. Also, .the raised bosses 13 are formed with generally flatplanar surfaces for receiving the filter cloths in a smooth manner. Theelements 6 preferably have a larger area on their internal sides than ontheir external side sides so that a greater area is provided fordistributing the force over the portion of the filter cloth between thespacing elements 6 and the plane raised surface of the boss 13. In apreferred embodiment of the invention the spacing elements are in theshape of a truncated cone with the larger side against the filter cloth3.

As illustrated in H6. 5, the height 14 of the spacing elements 6 shouldbe lower than the height of the frame members 5 so that in thecontacting but unloaded position of adjacent filter plates a space 10remains between the spacing elements 6 and 6'. Consequently, theelements 6 and 6' will not contact each'other until a pressuredifferential force comes into existence during the pressing operation.Preferably, the space 10 I should be between 0.l and 0.5 mm., and inparticular, between 0.1 and 0.3 mm. Further, all of them the spacing elements on a given surface should be of substantially the same height witha tolerance of up to 0.3 mm. but preferably 0.2

Although the invention has been described inconsiderable detail withrespect to a preferred embodiment thereof, it will apparent that theinvention is capable of numerous modificachamber, an influent inletopening in said inner portion for introducing influent liquid to thesaid filter chamber, a means for discharging filtered liquid to the saidfilter chamber, a means for discharging filtered liquid from the filterchamber formed between two adjacent plates, said filter plate havingslightly raised, generally flat bosses formed on each opposite side ofsaid inner portion in alinement with each other and at a locationbetween and spaced from both the influent inlet opening and the saidframe, a passage through the said inner portion extending from thesurfacerof one generally fiat boss to the surface of the other saidgenerally flat boss which is alined therewith, a filter cloth extendingover the surface of each side of said inner portion and lying flatagainst the raised surfacesof said bosses, a hollow pin passing throughsaid passage and through said filter cloths, a spacing element on eachside of said inner portion. said spacing'element including a generallyflat surface facing the filter plate, the height of each spacing elementabove the center plane being less than the height of the frame above thecenter plane, and means for attachingthe spacing elements to the saidpin such that the cloth on each side of the plate is pressed and thusheld betweenthe raised bosses and thespacing elements and such thatthetwo sides ofa filter plate may be placed in fluid communication witheach other through said passage and through said pin.

2. A filter plate according to claim I wherein said pin is in the formof an outwardly expanding, elongated split ring, whereby the outwardresilience of the pin holds it against the said aperture.

3. A filter plate according to claim 1 wherein the height of eachspacing element above the center plane of the plate is approximately.05mm. to .25mm. less than the height of the frame from the said centerplane, whereby in the rest position, alined spacing elements of twoadjacent contacting plates will be separated by approximately 0.1 to 0.5mm.

4. A filter plate according to claim 3 wherein each side of the innerportion includes a plurality of spacing elements, the height of all saidspacing elements from said center plane being substantially equal toeach other and within a tolerance ofplus or minus 0.2 mm.

6 5. A filter plate according to claim 1 wherein the area of the 7. Afilter press comprising end plates, a plurality of filter side of thespacing element against the filter cloth is larger plates mountedadjacent each'other between said end plates to than the area of theoutermost end of the spacing element. be pressed together when the endplates are moved towards A fil plate according to claim 5 wherein thespacing each other, each said plate constructed according to claim 1.element is in the form of a truncated cone. 5

